Measurement of antibody binding to their specific antigen by direct electrochemical transduction has great potential as an analytical technique in the health care area. However, antibody-antigen interactions are difficult to detect due to the subtlety of the signal (no new product generated). AC impedance spectroscopy is a promising but underdeveloped technique which they propose to explore in basic detail, using a combination of antigen with three forms of a monoclonal antibody: whole IgG, whole IgG conjugated with colloidal gold and F(ab)2 fragments of IgG. Changes in the capacitance of the heterostructure upon complexing of antigen to the antibodies will be compared to that of the immobilized antibodies alone, using three electrode impedance measurement. The specificity of the surface changes observed (specific binding activity) will be assessed by simultaneous DC resistivity measurements of antibody recognition reactions, while minimizing or negating non-specific interferences. In turn, this will allow simplification of the instrumentation required, permitting the construction of practical direct biosensors in Phase II study. The development of biosensors utilizing biorecognition probes will have broad applicability in many areas, including health care, food quality control and detection of environmental contaminants.